In order to screw or unscrew threaded connecting elements, and more particularly large-size connecting elements consisting, for example, of bolts, automatic means are used, such as screwing and unscrewing robots.
The bolts are generally provided with a special connector which may be locked directly onto the nose of the screwing, or unscrewing robot.
In certain cases, the bolts do not have this special connector, with the result that it is necessary to insert an adaptor between the robot and the upper end of the bolt.
This is the case in particular for nuclear-reactor vessel bolts which are of the short type and do not have the special connector for interconnecting the robot and the bolt.
This adaptor serves to transmit the torque for the screwing or unscrewing to the bolts, but also to unlock the bolt from its position when difficulties are experienced in unscrewing it.
These difficulties may be the result, either of the threads being clogged up, or, of a mechanical stiff point. In the first case, it has been noted that, for effective action, the unscrewing torque must be greater than that initially provided.
This state of affairs gives rise, in the region of the connection joining the robot to the threaded connecting element, to supplementary and hence parasitic forces.
In the second case, the situation is particularly delicate. The origination of the mechanical stiff point may be caused either by the presence of an isolated hard body lodged between the threads or by creep caused by excessive clamping force or alternatively a force during use.
Whatever the type of anomalies to be eliminated, the adaptors used to date do not enable the problem to be solved effectively and generally require a fairly long service time, which may be prejudicial to the safety of the people responsible for these operations as they may be carried out in an area often made dangerous by the fact that it is subjected to high levels of radiation or to chemical pollution.